The UK opposition has warned of “a summer of chaos and confusion” as it challenged Boris Johnson to set out clearly the likely fallout of the government’s plan to end most Covid-19 restrictions in England on July 19.

Sir Keir Starmer, the Labour party leader, said businesses and families would face “huge disruption” in the coming weeks; millions of people could be told to self-isolate in the face of Covid-19 cases rising to an estimated 100,000 a day.

Johnson declined to tell Starmer the numbers for hospitalisations, long Covid cases and deaths the government was expecting as it prepared to lift most remaining legal restrictions.

“He is taking all protections off in one go,” Starmer said at prime minister’s questions in the House of Commons. “That is reckless.”

Starmer referred to the Financial Times report that 2m people a week could be at risk of contracting Covid-19 or being asked to self-isolate after coming into close contact with somebody who had tested positive.

Sajid Javid, health secretary, has said cases could rise to 100,000 a day — far exceeding the previous January peak of 61,240 — after restrictions are lifted.

Recent data suggest two people are asked to isolate for 10 days for every original case, suggesting that, on top of the 700,000 people potentially infected in a week, a further 1.4m could be required to stay at home.

Johnson declined to say how many people he expects to be forced into isolation before quarantine rules change on August 16, when double-jabbed people and under-18s will no longer have to self isolate if they come into close contact with someone with Covid-19.

Speaking at a parliamentary select committee, Johnson said the extra weeks would allow “much more progress on vaccination”.

“All these decisions are a balance of risk. We will have many more jabs into people’s arms [by then], which is a good thing,” he said.

In a sign of unease in government over the policy, business secretary Kwasi Kwarteng said waiting until August 16 before easing self-isolation rules was “a balance, not a perfect solution”.

Iain Duncan Smith, former Conservative leader, told the Daily Telegraph he would not go to a pub that had no social distancing “otherwise you run the risk of everyone in the pub being pinged and locked down”.

But the prime minister insisted he was taking a “balanced and reasonable approach”. Ministers will decide on July 12 whether to press ahead with the ending of most legal restrictions on July 19.

Johnson added: “Scientists are also absolutely clear that we have severed the link between infection and serious disease and death.” Sir Patrick Vallance, chief scientific adviser, said this week the link was weakened but “not completely broken”.

Kate Nicholls, chief executive of industry body UKHospitality, has said self-isolation rules were causing “carnage” in her sector, with up to one in three staff forced to stay at home at any given time.

She said that if the situation deteriorated then hotels, bars and restaurants would be “unable to service demand through the summer trading period”, adding that younger workers who had not been fully vaccinated would be particularly badly hit.

Nicholls is urging ministers to consider introducing a “test to release” scheme that would allow people to end self-isolation after five days if they test negative.

Health bosses also fear severe staff shortages in hospitals, which are trying to clear a treatment backlog but face a rise in Covid cases at a time when many staff are taking annual leave and others may now be forced to self-isolate.